Brake



Jan. 5, 1932. 'r. T. GREENWOOD BRAKE Filed Aug. 10, 1928 2 13 r h h m J m W m w u m m 1e f H 1 W a Q Patented Jan. 5, 1932 UNITED ,srA'rE's. PATENT OFFICE rm r. enmwoon, ormsr mrmron, mssncnusnrrs Application filed August 10, 1928. Serial No. 298,895.

This invention relates to brakes, and especially to automobile brakes, which are' such that the composite coeflicientof friction, or brakin effort, is about the same,

I whether the bra e is dry or wet.

It is an object of the present invention to provide a brake utilizing the above principle, 0 -wherein a loss in friction of the brake is largely compensated for automatically in the application of the brake when it is wet.

further object is the provision of a brake wherein the rotation of the brake drum is caused largely to com ensate automatically for a loss in friction o the brake when it is wet. v Another object of the inventionis the pro- A yet further object of the invention is the provision of a brake of the servo type, wherein the servo or self-energized portion of the brake has a braking surface composed mainly of one material, as one that increases its coeflicient of friction when wet, and the other portion of the brake has a braking sur- Fig. 1- is a sectional elevation of a. brake copending application Serial No.

vision of a brake having means to multiplyface composed mainly of a difierent material, as one that decreases its coefiicient of friction embodying the present invention, taken along line 11 of Fig. 2.

Fig. 2 is a section along line 2,2 of Fig. 1. 7

Figs. 3 and 4 are sectional details taken Fig. 1.- 4

Fig. 5 is a view similar to Fig. 1 but illustrating a modified form of brake embodying the invention.

The brake illustrated in Figs. 1 and 2 is of the three-shoe, internal expanding servo, or selfvenergizing type, well known in the art, and including the op ositely-extended rigid shoes 10 and 12 pivoted at Hand 16 respectivel to arms 18 of a fixed bracket 20.

A rotatab e brake drum 22 encloses and is adapted to be engaged by said shoes. A third rigid or servo shoe 24 is pivoted at 26 to the free end of the shoe 10 and has its free end 28. confronting the free end 30 of the shoe 12. Suitable operating mechanism, here shown as a rotatable cam 32 is located between said confronting ends and is'adapted to spread them apart and into frictional engagement with the brake-drum. Due to the frictional en- '70 gagement between thedrum and the servo shoe, and, the rotation of the drum, said servo shoe is caused to press the shoe 10 forcibly against the brake drum with an efieet that is materially greater than that due solely to the action of the cam 32. The servo action thus multiplies the braking effort supplied by the cam. This action is well known and need not be further explained. 7

A spring 34 is extended between the free ends of the brake shoes 12 and 24 to hold them yieldingly-out of engagement with the brake drum w enthe cam 18 in normal or unoperated position. A second s ring 36 is connected with the brake shoe 10 or the same 55 purpose. p

The brake shoe 12 has a brake lining. 38 of suitable material. Thebrake'shoe 10 has a suitable brake lining 40 which say, is lso characterized that it hasits' ociiicient of respectively. along lines 33 and 44 of 60 .the frictional effort of the shoe is decreased and the shoe 24 is increased, whereby one tends to compensate for the other.- By reason of the. servo action, and its multiplying effect, a braking surface for the servo shoe can be used'which has a relatively small increase in frictional effect when wet and will com ensate for a relatively great decrease in rict-ional effect of the shoe 10 when wet, thus to maintain the total braking effect practically unchanged. For the same reason the braking area of the servo shoe can be less than that of the shoe 10. The braking surface of the two shoes, their areas, and characteristics are so chosenthat the combined braking efiect is practically the same, when the brake is dry or wet, or when subject to other diverse conditions.

In the modification illustrated in Fig. 5 the servo or self-energized brake is of the type having a flexible band 44 which is 10- cated within the brake drum 46 and has a fixed end 48 and a free end 50. The brake band is adapted to be forced or wrapped into frictional engagement with the drum by the drag of the rotating drum on it. In accordance with this invention the band 44 is provided with two dissimilar brake surfaces or linings 52 and 54 which have the characteristics of the linings 40 and 42 as above set forth and which functions in the same manner.

In either case it is not important which of thebraking surfaces is the one that has itscoefficient of friction, or braking effort, increased when wet as the action is the same for, if the surface 40, or 52, increases its frictional effort when wet, the reduced effect of the surfaces 42, or 54, is to decrease the pressure thereon and to keep the braking effect practically constant.

I claim:

1. A brake having the combination of a rotary member, a'brake member engageable therewith the frictional effect of which is different when the brake member is wet and dry, and operating mechanism for said brake member including means operated by said rotary member to apply on said brake member an actuating pressure which compensates for variation in the frictional character of said brake member under diverse conditions of wetness .to such extent that the braking effect is practically the same whether the brake is wet or dry.

2. A brake having the combination of a rotary member, a brake member en ageable therewith subject to a variable bra ing effeet under diverse degrees of wetness, and means tending to compensate for said variable braking effect, including means to multiply the compensating effect of said first means to such extent that the braking effect is practicallythe same whether the brake is wet or dry.

3. A brake having the combination of a rotary member, a brake member engageable therewith subject to a variable braking effeet under different degrees of wetness, means acted on by said rotary member adapted automatically to compensate for said variable braking effect and having means to multiply the compensating effect of said first means to such an extent that the braking effect of said brake member and said first means is the same when the brake is wet or dr Z. A brake having the combination of a movable member, two brake members for retarding the movement of said movable member, and means for increasing the retarding effect ofone brake member upon decrease of retarding effect of the other brake member to such extent when they are both subject to wetness that their combined effect remains the same whether they are wet or dry.

5. A brake having the combination of a movable member, two brake members for retarding the movement of said movable member, and means which var the retarding effect of said brake mem ers o positely to such extent when the brake is suB1ect to wetness that their combined effect is the same whether wet or dry. I

6. A brake having the combination of a brake drum, two brake members acting thereon which have oppositely varying braking effects on said drum when sub ected conjointly to wetness and means to enhance the variable braking effect of one member on said drum through said other member to such extent that the combined action of the brake members is the same whether they are wet or dry. 7. A brake having the combination of a brake drum, two brake members acting thereon which have oppositely varying braking effects on said drum when subjecte conjointly to wetness that their combined effect is practically the same whether wet or dry, and means whereby one of said brake members urges the other brake member against said drum by the rotation of said drum. 7

8. A brake having the combination of a brake drum, two brake members bearing internally on said drum, and means connecting said members whereby the drag of the drum on one member forces the other member against the drum, said brake members having means which provides oppositely va ing braking effects to such extent when'su jected conjointly to wetness that their combined effect is practically the same whether wet or dry.

9. A brake having the combination of a brake drum, a brake member acting thereon, and a servo brake member acting on said 1 drum and also on the aforesaid brakememher, said brake members having oppositely varying frictional engagement with said drum to such extent when sub'ected conjointly to wetness that their com ined effect is practically the same'whether wet or dry.

brake drum, a pivoted brake shoe acting on said drum, and a second shoe acting on said drum and also on said pivoted shoe in a direction to force it against saiddrum, said shoes having frictional engagement with said drum which vary oppositely when subjected con- 4 jointly to different conditions of wetness that their combined efiect is practically the same whether the shoes are wet or dr brake drum, a pivoted brake shoe acting on said drum, and a second shoe acting on said drum and also on said pivoted shoe in a direc-' tionto force it against said drum, said shoes so having frictional engagement with said drum which vary oppositely when they are wet and 1 in such relative degree that the action of said shoes on said drum is practically constant (liegardless of whether the shoes are wet or 85 r 2. A brake having the combination of a brake drum, a pivoted brake shoe acting on I said drum, and a servo shoe actin on said pivoted shoe and on said drum, sai pivoted shoe having a frictional engagement with said drum which varies with diverse operating conditions of wetness, and said servo shoe having a frictional engagement with said brake drum and an action on said pivoted shoe which varies in an opposite manner to thatof said pivoted shoe and toa degree to maintain the braking efiect of both shoes practically constant whether the brake is wet or dr drum, a brake shoe therefor, and a servo shoe having an actuating connection with the brake shoefsaid brake and servo shoes having friction face-materials characterized by one having decreased and the other increased frictional efiect whenwet and pres- 10. A brake having the combination of" a v i 11. A brake having the com ination of a it 13. A brake having the combination of a can 3 ing a reduced frictional eflect when wet,"a servo shoe havin an actuating connection with said brake s 'oe and'a linin which engages said drum and is characterized by having an increasedfrictional effect when wet, said two linings being present in such proportions and' said actuatln' connection being such that the combined rictional efiect of the two shoes on the drum is the same whether the linings are wet or dry. In testimony whereo name to this specification.

. TALMA T. GREENWOOD.

, I havesigned my ent in such proportions" and reacting one 'with the other through said actuatin connection to such extent that the combine tional effect of the shoes on the drum is practically the samewhether the shoes are wet or dry.

14. A brake having the combination of a drum,a brake shoe having a lining which engages said drum and is characterized by hav-;

fric 

